How Chrome Plating Resists Wear on Moving Parts
Moving parts wear out at the surface. By applying the right coating the rate of wear can be considerably reduced.
Extreme Surface Hardness
Chromium deposits have extreme surface hardness values between 850 to 1,000 HV. As chrome plated components are often of engineering steel, the hardness of the surface is significantly greater than the parent material, thus providing excellent wear resistance when other parts move over it.
Low Friction at Sliding Interfaces
The coefficient of friction for chrome against steel in a lubricated condition is typically around 0.15 – 0.2. This low friction value means that there is less friction at the surface of parts that have been chrome plated. This in turn means that there is less heat generated at the surface of the parts during normal operation. This in turn means that there is less chance of thermal fatigue and of wear between the surfaces of parts that are in contact with each other.
The Crack Network That Holds Lubricant
Chromium plating creates a fine crack network on the surface. This crack network fills with lubricant, to keep it on the surface between contact cycles, thus keeping the maximum amount of lubricant between sliding parts.
Resistance to Pitting and Surface Corrosion
Small surface flaws, such as pits or corrosion, can become stress concentrators under cyclic loading and can cause localized cracking or spalling, which in turn can cause rapid wear. The surface of a chrome plated part is resistant to pitting and corrosion, thus reducing the number of sites where wear can initiate and progress.
Matching Deposit Thickness to the Application
The thickness of the chrome plating deposit is usually specified as being required to meet a particular wear characteristic or part tolerance. For example, a seal used on a hydraulic ram could be specified to be 25 to 75 microns thick, while a shaft journal running under heavy load could require a thicker deposit. It is critical that the correct thickness is specified from the design stage to avoid both under-coating and subsequent rework.
Specifying the correct thickness at the design stage can save much time in the workshop.
